When holes are being drilled for exploration, rock and soil sampling, water, oil, gas, or geothermal developments, there is often a need to seal or stabilize the walls of the borehole, cement in casing pipes, or seal portions of the well at some depths while other portions at other depths are treated or produced. Drilling programs for multilateral, horizontal or deviated wells often require that portions of a wellbore be sealed or plugged. Also, after casing, the elbow areas where lateral wellbores depart from the vertical hole are often the sites of loss of fluids into the surrounding formation. This fluid loss is often caused by high pressures encountered in the deviated production path, and exacerbated by mechanical failures of bonding materials at the lateral junction.
Drilling-related problems such as lost circulation, water shutoff, and swelling, sloughing or caving of the borehole walls have been dealt with by introducing various materials into the borehole to seal or stabilize the borehole, or to clog pores or fractures in the surrounding rock formation or to fill and stabilize cavities or washouts. These materials include various fibrous materials added to the drilling fluid or cement compounded with various additives.
Generally, cement-based materials do not bond well to the earth materials penetrated by the borehole and often do not stay in place. In addition, there are often problems getting these materials applied at precisely the desired depths and adapted to the particular downhole conditions in the trouble zone, particularly in severe lost circulation situations where cement materials tend to be overdisplaced away from the near-wellbore region. Further, with cement-type materials there can be difficulty judging appropriate pumping times and setting times at the elevated temperatures that are encountered in geothermal or very-deep petroleum drilling situations.
Furthermore, if the formation or fracture zone is severely underpressured or the formation contains large open porosity (e.g., interconnected large solution cavities in limestone formations), sealing the trouble zone by injecting cement from the surface is often unsuccessful. It is often unsuccessful no matter how many times the sealing operation is repeated because the hydrostatic head of the cement slurry causes the cement to be overdisplaced (i.e., carried away) from the near-wellbore region where the sealing is desired.
Another common approach used when there is a need to seal the borehole at certain depths while drilling is to circulate drilling fluid (mud) containing lost-circulation material to affect a temporary-to-permanent seal of the borehole wall as the drilling fluid permeates the formation or fracture zone. However, fibrous lost-circulation materials being carried in the drilling fluid may not adequately bridge-off the fractures or fill the open porosity because of the large outward pressure gradient from the overpressured borehole into the severely underpressured formation. This condition is referred to as severe lost circulation.
When there is a need to stabilize poorly consolidated or loose and friable formations at certain depths, where caving or sloughing produces cavities (“wash-outs”) and attendant borehole stability problems, this again has traditionally been done by pumping portland cement from the surface to fill and stabilize the borehole.
Subsequently, the borehole is redrilled through the soft cement plug and drilling then continued. However, since portland cement does not adhere well to most geologic materials, the typical result is to “wash” the cement out of the borehole and cavity while redrilling. With the cement washed out of the borehole, the cavity is reopened and additional caving or sloughing occurs. Then, the cementing operation is repeated over again until either a good plug is finally established, or the operator finally resorts to running and cementing a string of steel casing pipe through the trouble zone. Running casing reduces the size of the hole that can be drilled below the cased-off interval.
When there is a need to stabilize and support the wellbore at certain depths where squeezing (i.e., plastic deformation and flowing of formations such as serpentines or plastic clays) is encountered, the only engineering solution has been to finish the drilling (often with multiple redrilling or reaming operations) as fast as possible, then run and cement a string of casing across the trouble zone. This remedial solution relies on the collapse strength of the casing to hold back the squeezing formation and reduces the size of the hole that can be drilled below the cased-off interval.
Similarly, when swelling clay (hydrating) formations are encountered in drilling, the standard remedial approach is to prevent water-based fluids from penetrating or reacting with the clays and causing swelling by: (a) forming an impervious “wall cake” on the wall of the borehole; or (b) adding potassium chloride to the drilling fluid to make it less reactive with the clays; or (c) switching to a hydrocarbon-based drilling fluid, which is, however, generally undesirable because of increased costs, difficulties of cleanup and environmental hazards. Again, casing off the trouble zone is a typical solution.
Thus there is still a need for effective ways of sealing, stabilizing or plugging boreholes under severe conditions. There is also a need for sealing, stabilizing and plugging materials with a capability for bonding tightly to earth materials, steel casing and to the sealing, stabilizing and plugging materials themselves. There is a further need for materials that can be tailored for the downhole conditions associated with the problem to be remedied and that can be applied to precisely the selected depths.
Therefore, it is an object of this invention to provide a composition and method for sealing, stabilizing or plugging boreholes at selected depths.
It is another object of this invention to provide a composition for sealing, stabilizing or plugging boreholes that can be tailored to the viscosities and setting temperatures mandated by downhole conditions without compromising the properties of the cured material.
It is a further object of this invention to provide a composition for sealing, stabilizing or plugging boreholes that binds strongly to the composition itself and to underground formations, steel and ceramics.
It is yet a further object of this invention to provide a composition and method of making the composition for sealing, stabilizing, supporting and plugging lateral junctions in multilateral boreholes.
It is also an object of this invention to provide a composition and method of making compositions for sealing, stabilizing or plugging applications in offshore drilling operations.
It is yet another object of this invention to provide a method of applying the invention compositions for sealing, stabilizing or plugging boreholes downhole.
Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.